Such ejectors are known, for example, from German Patent DE 43 02 951 C1, and operate in accordance with the Venturi principle. The pressure gas, compressed air as a rule, which is filtered and free of lubricant, flows through a connector into the ejector and reaches the propellant nozzle, in which the flow speed of the air is increased to supersonic speed in the narrowed part. Following the exit from the propellant nozzle, the air is expanded and flows into the diffuser, and from there into the open, possibly via a muffler. In the process a vacuum is created in the chamber surrounding the propellant nozzle, which results in air being aspirated via the suction connector. The aspirated air and the propellant introduced into the jet pump move into the open together via an expansion section.
In comparison with other vacuum pumps, such ejectors have the advantage of having no rotating parts and therefore have low maintenance and wear properties. They are furthermore explosion- protected, since they are of a purely pneumatic nature. They moreover are of simple construction and can be installed in any desired position. They do not generate heat and can be switched in, or respectively out, at any time, which results in energy savings. It is furthermore possible to build up the vacuum more quickly because of the short lengths of the lines between the suction gripper and the ejector. Finally, the compact construction, the low weight and the option of combining several functions in one apparatus have a great importance in the fields of ready-made clothes, work preparation, sales, mechanical processing, assembly, startup and spare parts supply.
When grasping larger components, several suction grippers are employed as a rule, which may be connected together into one ejector. However, several injectors are usually employed for this. These several ejectors are combined, for example in a sandwich construction, into a unit. Several vacuum circuits can be formed by means of this unit. However, it has been shown that disadvantages have occurred in spite of the use of these ejectors, since the ejectors continue to be connected with the suction grippers by means of hose assemblies, and the ejectors, in particular the shut-off valves contained in them, must be actuated via electric lines. Both the hose assemblies and the electric lines have interfering effects and possibly hinder the grasping of the object to be transported. The construction as well as the maintenance of such units is relatively elaborate, or respectively cumbersome, since the ejectors must either be directly connected with each other via seals, or spacers are interposed between the ejectors, and the entire unit must be disassembled in case of repairs or maintenance. Such units are moreover relatively expensive, since additional components, such as seals, connecting elements, etc. are required besides the individual complete ejectors.